(a) Field of the Invention
The present invention relates to a method of efficiently recharging a supplementary battery of a vehicle, and more particularly, to a method that can recharge the supplementary battery with power from a main battery, and a recharging system for performing the same.
(b) Description of the Related Art
A vehicle is started using a battery voltage, and instruments such as indoor lamps and electrical devices such as an air conditioner of the vehicle are provided with power from a battery and a generator. When an engine of the vehicle is driven by rotating a starter motor to start the vehicle, an AC generator coupled to the engine through a fan belt generates electricity so as to recharge the battery.
In the case of an electric vehicle (EV) or a hybrid vehicle (PHEV/HEV), a motor thereof performs energy regeneration and torque supplement, and a main battery provides power. The main battery provides a high voltage (e.g., about 330V), in general. An electric car is provided with a supplementary battery in addition to the main battery. The supplementary battery provides power to operate an electrical switch for supplying a high voltage of the main battery to a motor control unit (MCU) or serves as a buffering device for voltage balancing in operations of devices driven by a low voltage (e.g. 12V) in the vehicle.
In particular, the main battery supplies power to the motor and devices in the vehicle, which are driven by electricity, after the vehicle is started. The supplementary battery provides power to operate an electrical switch for supplying a high voltage of the main battery to a motor control unit (MCU) or serves as a buffering device for voltage balancing in operations of devices driven by a low voltage (e.g. 12V) in the vehicle. The supplementary battery can be recharged by a low voltage DC-DC converter (LDC) that converts the voltage of the main battery to a low voltage. When the LDC recharges the supplementary battery, the output voltage of the LDC is controlled according to supplementary battery charging current. A supplementary battery charging logic will now be described with reference to FIGS. 1A-1B (RELATED ART).
FIGS. 1A and 1B illustrate an exemplary logic for controlling charging of a supplementary battery of a vehicle.
In FIGS. 1A and 1B, the charging control logic controls an LDC voltage by applying a current limit Batt Current Limit and a cancellation current limit Cancellation Batt Current Limit to current battery charged current Batt Current Filtered.
Referring to FIG. 1A, when a state that the current battery charged current Batt Current Filtered is greater than the current limit Batt Current Limit continues for a predetermined monitoring period (e.g. N=10 seconds), the LDC decreases the output voltage (i.e. target voltage) by 1 step (e.g. 0.1 V). The procedure is repeated at a monitoring interval.
When the current battery charged current Batt Current Filtered is lower than the Cancellation Batt Current Limit, as shown in FIG. 1B, voltage control is cancelled and thus the target voltage is set to a default LDC voltage. Here, the default LDC voltage may be fixed or controllable according to the state of the supplementary battery, for example, state of charge (SOC) and/or temperature of the supplementary battery.
When the logic as shown in FIGS. 1A and 1B is applied, charging current exceeds the current limit for a long time if recharging of the supplementary battery which has been discharged is started, and thus the target voltage is stepped down several times and a difference between the target voltage and the default LDC voltage increases. Here, battery charged current decreases upon completion of recharging of the supplementary battery and voltage control is canceled when the battery charged current is reduced below the cancellation current limit, and thus the target voltage stepped down several times is recovered to the default LDC voltage. When such situation is repeated, supplementary battery life is decreased.